resolvers: fix empty sshd validation command in post-quantum task

The 'Validate sshd configuration' task had ansible.builtin.command with no
command, so it always errored (one of the following is required:
_raw_params, cmd, argv), tripping the rescue that reverts the drop-in. The
post-quantum KexAlgorithms hardening therefore never applied. Run sshd -t
to validate before restart as intended.

ansible/roles/resolvers/tasks/main.yml

@@ -81,7 +81,7 @@
       register: pq_sshd_dropin
 
     - name: Validate sshd configuration
-      ansible.builtin.command:
+      ansible.builtin.command: /usr/sbin/sshd -t
       changed_when: false
 
     - name: Restart sshd to apply key-exchange change